Plasma spectroscopy analysis method

ABSTRACT

The disclosure provides plasma spectroscopy analysis methods using a preparatory process of diluting a urine sample assumed to contain mercury or lead as an analyte metal species, and then adding a known concentration of thallium as a control metal species to the diluted urine sample; a concentration process of introducing the urine sample containing the control metal species to a measurement container, and applying an electric current across a pair of electrodes disposed in the measurement container to concentrate the analyte metal species and the control metal species present in the urine sample in a vicinity of at least one of the electrodes; a detection process; a correction process; and a quantification process.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese PatentApplication No. 2017-131940, filed on Jul. 5, 2017, the disclosure ofwhich is incorporated by reference herein.

BACKGROUND

Technical Field

The present invention relates to a method for quantifying mercury orlead in a urine sample by concentrating the mercury or the lead in thesample at an electrode via stripping and by performing plasmaspectroscopy.

Related Art

A method for quantifying heavy metal ions in a sample is disclosed in JP2016-130734 A, in which the heavy metal ions in a sample areconcentrated at an electrode via stripping, a large electric current issubsequently applied such that the heavy metal ions exhibit plasmaemission, and the heavy metal ions in the sample are quantified usingthe amount of emitted light.

SUMMARY

Depending on characteristics and conditions of samples, the samplesoften exhibit variation in the amount of plasma emission for identicalconcentrations of heavy metal ions. Quantification accuracy may sufferas a result of such variation in emission amounts.

As to urine samples, particularly, such variation in emission amounts isassumed to be caused by endogenous substances in the urine samples.

An object of an exemplary embodiment of the present invention is toimprove the accuracy of quantification by suppressing such variation inemission amounts.

A plasma spectroscopy analysis method of an exemplary embodiment of thepresent invention includes a preparatory process, a concentrationprocess, a detection process, a correction process, and a quantificationprocess. In the preparatory process, a urine sample assumed to containmercury or lead as an analyte metal species is diluted, and then a knownconcentration of thallium as a control metal species is added to thediluted urine sample. In the concentration process, the urine samplecontaining the control metal species is introduced to a measurementcontainer, and an electric current is applied across a pair ofelectrodes disposed in the measurement container to concentrate theanalyte metal species and the control metal species present in the urinesample in a vicinity of at least one of the electrodes. In the detectionprocess, an electric current is applied across the pair of electrodesafter the concentration process so as to generate plasma, and emittedlight from the analyte metal species and the control metal speciesarising due to the plasma is detected. In the correction process, acorrected value is calculated by correcting an analysis emission amountthat is a net emission amount at an analysis wavelength corresponding tothe analyte metal species detected in the detection process, using acontrol emission amount that is a net emission amount at a controlwavelength corresponding to the control metal species detected in thedetection process. In the quantification process, the analyte metalspecies in the urine sample is quantified by comparing the correctedvalue to a calibration curve obtained by advance measurements of knownconcentrations of the analyte metal species.

In the plasma spectroscopy analysis method of the exemplary embodimentof the present invention, an analyte metal species is quantified bycorrecting a plasma emission amount due to mercury or lead as theanalyte metal species using a plasma emission amount due to a knownconcentration of thallium as the control metal species. Thecharacteristics and state of the urine sample affect the plasma emissionamount of the thallium. However, the arising plasma emission amountcorresponds to the known concentration of thallium. Standardizing (forexample, “dividing”) the plasma emission amount due to the mercury orlead using the plasma emission amount corresponding to the knownconcentration of thallium accordingly enables the effect of thecharacteristics and state of the urine sample to be eliminated to themaximum extent. Namely, variation in emission amounts due to thecharacteristics or state of the urine sample are suppressed, therebyimproving the accuracy of quantification of the mercury or lead whenusing the plasma spectroscopy analysis method.

In such a process, endogenous substances contained in the urine sample(in particular creatinine) may cause variation in the plasma emissionamount of the thallium, which might actually cause accuracy to suffer,rather than improving the accuracy of quantification as described above.However, diluting the urine sample eliminates the effects of suchsubstances to the maximum extent possible.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will be described in detail based on the followingfigures, wherein:

FIG. 1A is a schematic see-through perspective view illustratingrelevant portions of a measurement container employed in an exemplaryembodiment of the present invention.

FIG. 1B is a schematic cross-section as viewed along the directionindicated by I-I in FIG. 1A.

FIG. 2A is a schematic cross-section for giving an overview of aconcentration process of plasma spectroscopy analysis employing themeasurement container illustrated in FIG. 1A.

FIG. 2B is a schematic cross-section for giving an overview of adetection process.

FIG. 3 is a schematic diagram illustrating an emission spectrum obtainedin a detection process.

FIG. 4A illustrates an emission spectrum for mercury.

FIG. 4B illustrates an emission spectrum for lead.

FIG. 5A to FIG. 5D are scatter diagrams illustrating correspondencerelationships between reference measurement values and convertedconcentration values in mercury measurements.

FIG. 6A to FIG. 6D are scatter diagrams illustrating correspondencerelationships between reference measurement values and convertedconcentration values in lead measurements.

FIG. 7A illustrates an emission spectrum for thallium, serving as acontrol metal species.

FIG. 7B is an enlargement of a characteristic peak in the vicinity of acontrol wavelength of 276 nm in FIG. 7A.

FIG. 7C is an enlargement of a characteristic peak in the vicinity of acontrol wavelength of 351 nm in FIG. 7A.

FIG. 7D is an enlargement of a characteristic peak in the vicinity of acontrol wavelength of 378 nm in FIG. 7A.

DETAILED DESCRIPTION

As described above, the plasma spectroscopy analysis method of anexemplary embodiment of the present invention includes a preparatoryprocess, a concentration process, a detection process, a correctionprocess, and a quantification process. In the preparatory process, aurine sample assumed to contain mercury or lead as an analyte metalspecies is diluted, and then a known concentration of thallium as acontrol metal species is added to the diluted urine sample. In theconcentration process, the urine sample containing the control metalspecies is introduced to a measurement container, and an electriccurrent is applied across a pair of electrodes disposed in themeasurement container to concentrate the analyte metal species presentin the urine sample in a vicinity of at least one of the electrodes. Inthe detection process, an electric current is applied across the pair ofelectrodes after the concentration process so as to generate plasma, andemitted light from the analyte metal species and the control metalspecies arising due to the plasma is detected. In the correctionprocess, a corrected value is calculated by correcting an analysisemission amount that is a net emission amount at an analysis wavelengthcorresponding to the analyte metal species detected in the detectionprocess, using a control emission amount that is a net emission amountat a control wavelength corresponding to the control metal speciesdetected in the detection process. In the quantification process, theanalyte metal species in the urine sample is quantified by comparing thecorrected value to a calibration curve obtained by advance measurementsof known concentrations of the analyte metal species.

The plasma spectroscopy analysis method according to the presentexemplary embodiment quantifies mercury or lead using a emission amountfrom plasma emission. A urine sample is introduced to a measurementcontainer in which a pair of electrodes are disposed. First, apredetermined electric current is applied across the electrodes (whichis referred to as “stripping”) to concentrate an analyte metal speciesin the vicinity of one of the electrodes. Thereafter, for example, alarger electric current than that employed in the stripping is appliedin order to cause plasma emission from concentrated mercury or lead asthe analyte metal species.

The preparatory process is a process in which the urine sample isdiluted, and thallium as a control metal species is added so as to be aknown concentration.

In the preparatory process, the urine sample may be collected andemployed as it is. However, in a case in which the concentration of anendogenous substance (such as creatinine) that affects the plasmaemission of thallium is too high, the urine sample may, for example, beemployed as a diluted liquid dissolved in a liquid medium. The liquidmedium is not particularly limited so long as it is capable ofdissolving the urine sample, and may, for example, be water or a buffersolution. In the preparatory process, in a case in which the endogenouscreatinine concentration is greater than 180 mg/dL, the urine sample maybe diluted such that the creatinine concentration is from 75 mg/dL to180 mg/dL. Alternatively, in the preparatory process, in a case in whichthe endogenous creatinine concentration is greater than 180 mg/dL, theurine sample may be diluted from 1.5 times to 3.5 times. In either case,it is necessary to dilute the urine sample to a degree so as to enablethe detection of plasma emission of mercury or lead while reducing theeffects of the endogenous substance.

The pH, for example, of urine sample may be regulated. The value of suchpH is not particularly limited so long as it assists detection ofmercury or lead. For example, the pH value of the urine sample may beregulated using a pH regulating reagent such as an alkali reagent or anacidic reagent.

Examples of alkali reagents include alkalis and aqueous solutions ofalkalis. Such alkalis are not particularly limited, and examples thereofinclude sodium hydroxide, lithium hydroxide, potassium hydroxide, andammonia. Examples of aqueous solutions of alkalis include an alkali thatis diluted in water or a buffer solution. The concentration of thealkali in such an alkali aqueous solution is not particularly limited,and may, for example, be from 0.01 mol/L to 5 mol/L.

Examples of acidic reagents include acids and aqueous solutions ofacids. Such acids are not particularly limited, and examples thereofinclude hydrochloric acid, sulfuric acid, acetic acid, boric acid,phosphoric acid, citric acid, malic acid, succinic acid, and nitricacid. Examples of aqueous solutions of acids include an acid that isdiluted in water or a buffer solution. The concentration of the acid insuch an acidic aqueous solution is not particularly limited, and may,for example, be from 0.01 mol/L to 5 mol/L.

The analyte metal species is mercury (Hg) or lead (Pb), and can exist ina charge-carrying state, for example an ionized state, in the urinesample. It is preferable that only one of the analyte metal species bepresent in the urine sample. However, since the characteristic peaksseen in the emission spectra differ in wavelength (analysis wavelength)and it is possible to distinguish between these peaks in emissionspectra, both analyte metal species may be present.

The urine sample may, for example, include a reagent to separate out theanalyte metal species in the urine sample. Examples of reagents includechelating agents and masking agents. Examples of chelating agentsinclude dithizone, tiopronin, meso-2,3-dimercaptosuccinic acid (DMSA),sodium 2,3-dimercapto-1-propanesulfonic acid (DMPS),ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA),ethylenediamine-N,N′-disuccinic acid (EDDS), and α-lipoic acid. In thepresent analysis method, “masking” refers to inactivating SH-groups, andmay, for example, be performed by chemically modifying SH-groups.Examples of masking agents include maleimide, N-methylmaleimide,N-ethylmaleimide, N-phenylmaleimide, maleimidopropionic acid,iodoacetamide, and iodoacetate.

The control metal species is thallium (T1) that is a metal species thatis different from the analyte metal species, and that can exist in acharge-carrying state, for example an ionized state, in the liquid urinesample. The characteristic peak exhibited by thallium at a controlwavelength in an emission spectrum can be distinguished from theanalysis wavelengths corresponding to peaks of mercury or lead as theanalyte metal species.

The control metal species is added to the diluted urine sample so as tobe a known concentration. The known concentration is not particularlylimited so long as it is a concentration that does not affect detectionof an analyte metal species assumed to be contained in the urine sample,and is a concentration at which the control metal species can beadequately detected. It is, for example, preferable that the controlmetal species may be added such that its final concentration in theurine sample is 100 ppb.

The concentration process is a process in which the urine sample isintroduced to the measurement container and an electric current isapplied across the pair of electrodes disposed in the measurementcontainer so as to concentrate the analyte metal species and the controlmetal species in the urine sample in the vicinity of at least one of theelectrodes.

The “pair of electrodes” refers to a combination of a cathode and ananode in electrolysis. The electrodes are solid electrodes, andspecifically, may be rod electrodes or the like. The electrode materialis not particularly limited, and any appropriate solid electricallyconductive material may be employed therefor according to the analytemetal species and the control metal species. The electrode material may,for example, be a nonmetal, may be a metal, or may be a mixture of anonmetal and a metal. In a case in which the electrode material includesa nonmetal, the electrode material may, for example, include one type ofnonmetal, or may include two or more types of nonmetal. Carbon is anexample of a nonmetal. In a case in which the electrode materialincludes a metal, the electrode material may, for example, include onetype of metal, or may include two or more types of metal. Examples ofmetals include gold, platinum, copper, zinc, tin, nickel, palladium,titanium, molybdenum, chromium, and iron. In a case in which theelectrode material includes two or more types of metal, the electrodematerial may be an alloy. Examples of alloys include brass, steel,Inconel (registered trademark), nichrome, and stainless steel. The pairof electrodes may, for example, both be formed from the same material,or may be formed from different materials from each other.

The size of the electrodes is not particularly limited so long as theyare at least partially housed inside the measurement container. Notethat it is preferable for the size of the measurement container to be assmall as possible if attempting to produce a cartridge type measurementcontainer suitable for mass production. In such cases, the electrodesare also made smaller so as to correspond to the size of the measurementcontainer. Moreover, one or both of the pair of electrodes may bepre-installed as a unit in the measurement container, or alternatively,the electrodes may be inserted into the measurement container asappropriate when a measurement is to be taken.

The one electrode is the electrode where the analyte metal species andthe control metal species are concentrated, and is the cathode in thiscase.

As described above, the concentration process is a process in which, inthe presence of the urine sample, an electric current is applied acrossthe pair of electrodes to concentrate the analyte metal species and thecontrol metal species in the urine sample in the vicinity of the oneelectrode. The pair of electrodes are in contact with the urine sample.In the concentration process, the “vicinity of the one electrode” is notparticularly limited, and may for example be a range over which plasmais generated in the detection process, described later, such as thesurface of the one electrode.

In the concentration process, for example, a portion of the analytemetal species and the control metal species in the urine sample may beconcentrated in the vicinity of the one electrode, or the entirety ofthe analyte metal species and the control metal species in the urinesample may be concentrated in the vicinity of the one electrode.

In the concentration process, charge conditions of the pair ofelectrodes are preferably set such that the electrode employed indetection of the analyte metal species and the control metal species inthe detection process described below, namely the electrode where plasmais generated (also referred to hereafter as the “plasma generatingelectrode”) is the one electrode, and the analyte metal species and thecontrol metal species are concentrated at this electrode. Regarding thecharging conditions, the direction of the electric current should be setsuch that the one electrode (namely, the plasma generating electrode) isa cathode in the concentration process, since the analyte metal speciesand the control metal species are normally metal ions carrying apositive charge.

The concentration of the analyte metal species and the control metalspecies may, for example, be regulated by voltage. Accordingly, a personskilled in the art is capable of setting an appropriate voltage to causeconcentration (also referred to hereafter as a “concentration voltage”).The concentration voltage is, for example, at least 1 mV, and ispreferably at least 400 mV. The upper limit of the concentration voltageis not particularly limited. The concentration voltage may, for example,be constant, or may fluctuate. The concentration voltage may, forexample, be a voltage at which plasma is not generated.

The application duration of the concentration voltage is notparticularly limited, and may be set as appropriate according to theconcentration voltage. The application duration of the concentrationvoltage is, for example, from 0.2 minutes to 40 minutes, and ispreferably from 5 minutes to 20 minutes. The voltage may, for example,be applied across the pair of electrodes continuously, or may be appliedacross the pair of electrodes intermittently. Pulsed application is anexample of an intermittent voltage application. In a case in which theapplication of the concentration voltage is intermittent, theapplication duration of the concentration voltage may be the totalduration over which the concentration voltage is being applied, or maybe the total of the duration over which the concentration voltage isbeing applied and the duration over which the concentration voltage isnot being applied.

The voltage application unit employed to apply the voltage across thepair of electrodes is not particularly limited, and, for example, anyknown voltage supply device may be employed so long as the predeterminedvoltage can be applied across the pair of electrodes. In theconcentration process, the electric current applied across the pair ofelectrodes is, for example, set from 0.01 mA to 200 mA, preferably from10 mA to 60 mA, and more preferably from 10 mA to 40 mA.

As described above, in the detection process, a larger electric currentthan that applied across the pair of electrodes in the concentrationprocess is applied across the pair of electrodes so as to generateplasma, and light emitted by the analyte metal species and the controlmetal species arising due to the plasma is detected.

Note that the direction of the electric current in the detection processmay be the same as the direction of the electric current in theconcentration process. However, it is preferable for the voltageapplication unit to be formed so as to be capable of switching thedirection of the electric current during voltage application such thatthe direction of the electric current during plasma generation is theopposite direction to the direction of the electric current duringconcentration of the analyte metal species and the control metalspecies.

Specifically, since in the concentration process the analyte metalspecies and the control metal species are positively charged, thedirection of the electric current generated by the voltage applicationunit should be set such that the one electrode, serving as a plasmagenerating electrode, becomes the anode in the detection process.

The concentration process may run straight on into the detectionprocess, but does not have to run straight on into the concentrationprocess. In the former case, the detection process is performed at thesame time as the concentration process ends. In the latter case, thedetection process is performed no more than a predetermined durationafter the end of the concentration process. The predetermined durationis, for example, from 0.001 seconds to 1,000 seconds after theconcentration process, and is preferably from 1 second to 10 secondsafter the concentration process.

In the detection process, “plasma generation” refers to substantiveplasma generation, and specifically, refers to the generation of plasmathat exhibits substantive detectable emission in plasma emissiondetection. As a specific example, plasma emission is detectable using aplasma emission detector.

The substantive plasma generation may, for example, be regulated byvoltage. Accordingly, a person skilled in the art is capable of settingan appropriate voltage to generate plasma exhibiting substantivedetectable emission (also referred to hereafter as the “plasmageneration voltage”). The plasma generation voltage is, for example, atleast 10V, and is preferably at least 100V. The upper limit of theplasma generation voltage is not particularly limited. The voltage atwhich plasma is generated is, for example, a relatively high voltage incomparison to the voltage at which the concentration occurs.Accordingly, the plasma generation voltage is preferably a highervoltage than the concentration voltage. The plasma generation voltagemay, for example, be constant, or may fluctuate.

The application duration of the plasma generation voltage is notparticularly limited, and may be set as appropriate according to theplasma generation voltage. The plasma generation voltage applicationduration is, for example, from 0.001 seconds to 0.02 seconds, and ispreferably from 0.001 seconds to 0.01 seconds. The plasma generationvoltage may, for example, be applied across the pair of electrodescontinuously, or may be applied to the pair of electrodesintermittently. Pulsed application is an example of intermittentapplication. In a case in which the application of the plasma generationvoltage is intermittent, the application duration of the plasmageneration voltage may, for example, be the duration of a singleapplication of the plasma generation voltage, may be the total durationover which the plasma generation voltage is being applied, or may be thetotal of the duration over which the plasma generation voltage is beingapplied and the duration over which the plasma generation voltage is notbeing applied.

In the detection process, the generated plasma emission may, forexample, be detected continuously, or may be detected intermittently.Detection of the emitted light may be performed by, for example,detecting the presence of emitted light, detecting the intensity ofemitted light, detecting a specific wavelength, or detecting a spectrum.The detection of a specific wavelength involves, for example, thedetection of a particular wavelength emitted by an analyte during plasmaemission. The method of detecting emitted light is not particularlylimited, and, for example, a known optical measurement instrument suchas a Charge Coupled Device (CCD) or a spectroscope may be employedtherefor.

In the detection process, the plasma generation voltage may be appliedto the pair of electrodes, using the voltage application unit, at ahigher voltage than that employed in the concentration process. It ispreferable that the direction in which the electric current flows beopposite to that in the concentration process. In the detection process,since the plasma generation voltage is relatively higher than theconcentration voltage, the electric current across the electrodes largerthan that in the concentration process. The electric current may, forexample, be set from 0.01 mA to 100, 000 mA, and is preferably from 50mA to 2,000 mA.

The emission spectrum obtained due to the plasma emission in thedetection process may be expressed as a graph in which emission amountsare plotted against individual wavelengths over a predeterminedwavelength range. In the correction process, first, a net emissionamount corresponding to the analysis wavelength that is a wavelength inthe emission spectrum suitable for quantifying the analyte metalspecies, is taken as an analysis emission amount, and a net emissionamount corresponding to the control wavelength that is a wavelength inthe emission spectrum suitable for quantifying the control metalspecies, is taken as a control emission amount. In the correctionprocess, a corrected value is calculated by correcting the analysisemission amount using the control emission amount.

Note that the net emission amount for the analysis emission amountrefers to the emission amount at the analysis wavelength due solely tothe presence of the analyte metal species, and is a corrected emissionamount in which a peak emission amount as the apparent emission amountat the analysis wavelength is corrected using a base emission amount asa emission amount that is independent of the plasma emission of theanalyte metal species.

Moreover, the net emission amount for the control emission amount refersto a emission amount at the control wavelength due solely to thepresence of the control metal species, and is a corrected emissionamount in which a peak emission amount as the apparent emission amountat the control wavelength is corrected using a base emission amount as aemission amount that is independent of the plasma emission of thecontrol metal species.

A method of determining or computing the base emission amount may be setas appropriate according to the type of graph obtained for the emissionspectrum. For example, in the emission spectrum, in a case in which apeak emission amount obtained corresponding to a specific wavelength isa portion rising up from a flat portion of a graph of the emissionspectrum, the emission amount of the flat portion may be set as the baseemission amount.

Note that in a case in which values for control emission amounts differbetween urine samples containing the control metal species at the sameknown concentration, although the control emission amounts reflect thesame known concentration of the control metal species, the differencebetween the values is thought to arise due to differences in the stateof the urine samples, for example the types and concentrations ofcomponents present in the solution. Such states of the urine samples maynaturally also be expected to affect the analysis emission amounts ofthe urine samples. Thus, it is possible to eliminate the effect of thestate of the urine sample on the analysis emission amount to the maximumextent by correcting an analysis emission amount using a controlemission amount that reflects a constant known concentration. In thecorrection process, the method for correcting the analysis emissionamount using the control emission amount should be set as appropriateaccording to the type of graph obtained for the emission spectrum. Forexample, a value obtained by dividing the analysis emission amount bythe control emission amount may be taken as a corrected value.Consequently, the analyte metal species is quantified according to howmany times greater in magnitude the analysis emission amount is than thecontrol emission amount reflecting the known concentration.

The quantification process is a process to quantify the concentration ofthe analyte metal species in the urine sample based on the correctedvalue calculated in the correction process. Note that the concentrationof the analyte metal species may, for example, be quantified based on acorrelative relationship between corrected values and concentrations ofan analyte in solution. Such a correlative relationship may, forexample, be defined by a calibration curve obtained by plottingcorrected values, obtained by performing each of the aforementionedprocesses for reference samples in which the analyte metal species ispresent in known concentrations similarly to the case of the urinesample, against the concentrations of the analyte metal species in thereference samples. The reference samples are preferably a dilutionseries for the analyte metal species. Defining such a calibration curveenables reliable quantification.

In the plasma spectroscopy analysis method of the present invention, thepair of electrodes may be disposed inside a measurement container thatincludes a transparent section. In such cases, in the detection process,light emitted by the analyte metal species and the control metal speciescan be detected by a light receptor disposed so as to be capable ofreceiving the emitted light through the transparent section.

Explanation follows regarding an example of the measurement containeremployed in an exemplary embodiment of the plasma spectroscopy analysismethod of the present invention, with reference to the drawings. In thedrawings, the structure of each section may be simplified as appropriatefor ease of explanation. The relative dimensions of the respectivesections are schematic and may not be true to reality.

FIG. 1A is a schematic see-through perspective view illustrating ameasurement container 10 employed in the present exemplary embodiment.FIG. 1B is a schematic cross-section viewed along the directionindicated by I-I in FIG. 1A. As illustrated in FIG. 1A and FIG. 1B, themeasurement container 10 employed in the present exemplary embodimentincludes a pair of internal electrodes (a plasma generating electrode 20and a non-plasma generating electrode 30). The measurement container 10has a substantially circular cylinder shape with part of one side havinga planar shape as if it is cut away. This planar portion includes acircular transparent section 11. A light receptor 40 is disposed at theexterior of the measurement container 10 so as to be capable ofreceiving light emitted by the analyte metal species and the controlmetal species, via the transparent section 11, when light is generatedby applying an electric current across the plasma generating electrode20 and the non-plasma generating electrode 30. Moreover, the plasmagenerating electrode 20 is disposed parallel to a liquid surface 61 of aliquid urine sample 60, and a leading end of the plasma generatingelectrode 20 is disposed to contact the transparent section 11. Part ofa side face of the circular cylinder shaped non-plasma generatingelectrode 30 is disposed on the side face of the measurement container10 at a side opposing the transparent section 11 so as to intersect avertical direction at a right angle, and part of the non-plasmagenerating electrode 30 is exposed to the interior of the measurementcontainer 10. Namely, a length direction of the non-plasma generatingelectrode 30 and a length direction of the plasma generating electrode20 are positioned so as to be twisted with respect to one another. Theplasma generating electrode 20 is covered by an insulator 22. The urinesample 60 that contains the analyte metal species and the control metalspecies is introduced into the measurement container 10 so as to makecontact with the plasma generating electrode 20 and the non-plasmagenerating electrode 30.

In the present exemplary embodiment, the majority of the surface of theplasma generating electrode 20 is covered by the insulator 22. A portionthat is not covered by the insulator 22 is a liquid-contacting portion21.

In the present exemplary embodiment, the plasma generating electrode 20and the transparent section 11 contact each other. However, there is nolimitation to such a configuration, and, for example, the plasmagenerating electrode 20 may be disposed at a separation from thetransparent section 11. The distance between the plasma generatingelectrode 20 and the transparent section 11 is not particularly limited,and may, for example, be from 0 cm to 0.5 cm.

The material of the transparent section 11 is not particularly limited,and so long as it is a material that allows light generated by applyingan electric current across the plasma generating electrode 20 and thenon-plasma generating electrode 30 to pass therethrough, for example,may be set as appropriate according to the wavelengths of the generatedlight. Examples of materials of the transparent section 11 includequartz glass, acrylic resin (PMMA), borosilicate glass, polycarbonate(PC), a cyclic olefin polymer (COP), and polymethylpentene (TPX(registered trademark)). The size of the transparent section 11 is notparticularly limited, and may be set to a size that allows lightgenerated by applying an electric current across the plasma generatingelectrode 20 and the non-plasma generating electrode 30 to passtherethrough.

In the present exemplary embodiment, the measurement container 10 has abottomed circular cylinder shape with part of one side having a planarshape as if it is cut away along the length direction. However, theshape of the measurement container 10 is not particularly limited, andmay be any desired shape. The material of the measurement container 10is not particularly limited, and examples thereof include acrylic resin(PMMA), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC),polyethylene terephthalate (PET), and polystyrene (PS). In a case inwhich the measurement container 10 has a bottomed cylinder shape, thediameter of the measurement container 10 is, for example, from 0.3 cm to1 cm and the height of the measurement container 10 is, for example,from 0.9 cm to 5 cm. The urine sample 60 of 0.3 cm³ to 0.8 cm³ isintroduced to the measurement container 10.

The light receptor 40 is not particularly limited, and may, for example,be a known optical measurement instrument such as a CCD or aspectroscope. The light receptor 40 may also, for example, be atransmission section that transmits the emitted light to an opticalmeasurement instrument. Examples of transmission sections include atransmission path such as an optical fiber.

The manufacturing method of the measurement container 10 is notparticularly limited. For example, a molded body may be manufactured byinjection molding, or the measurement container 10 may be manufacturedby forming a recess in a substrate such as a plate. Otherwise, themanufacturing method of the measurement container 10 is not particularlylimited, and for example, lithography or machining methods may also beemployed.

Explanation follows regarding an overview of the plasma spectroscopyanalysis method of the present exemplary embodiment, in which mercuryions or lead ions as the analyte metal species are assumed to be presentin the aqueous solution of the urine sample 60.

First, after diluting the urine sample 60 as appropriate, a knownconcentration of the control metal species (namely, thallium ions) isadded to the diluted urine sample 60. Then, in a state in which theurine sample 60 is introduced to the measurement container 10, in theconcentration process, as illustrated in FIG. 2A, a voltage applicationsection 50 is used to apply a voltage with the plasma generatingelectrode 20 serving as a cathode and the non-plasma generatingelectrode 30 serving as an anode. Then, the mercury ions or lead ions,as well as the thallium ions, present in the urine sample 60 are drawntoward the liquid-contacting portion 21 of the plasma generatingelectrode 20 as the cathode.

Next, in the detection process, as illustrated in FIG. 2B, the voltageapplication section 50 is used to apply a voltage but with the plasmagenerating electrode 20 serving as an anode and the non-plasmagenerating electrode 30 serving as a cathode. Then, plasma emission isgenerated by the mercury ions or lead ions, as well as the thallium ionsdrawn to the vicinity of the liquid-contacting portion 21 of the plasmagenerating electrode 20 in the preceding concentration process. Thisplasma emission passes through the transparent section 11 and isreceived and detected by the light receptor 40.

Suppose that an emission spectrum obtained in the detection process isas illustrated in FIG. 3. Note that in FIG. 3, W₁ is the analysiswavelength, W₂ is the control wavelength, P₁ is the peak emission amountat the wavelength W₁, P₂ is the peak emission amount at the wavelengthW₂, B₁ is the base emission amount corresponding to the peak emissionamount P₁, and B₂ is the base emission amount corresponding to the peakemission amount P₂. The magnitude relationships between W₁ and W₂, andbetween P₁ and P₂, are not limited to those illustrated. Moreover,although B₁ and B₂ are illustrated as if they were the same values aseach other, there is no limitation thereto, and configurations in whichone is a greater value than the other are also possible.

In such a case, an analysis emission amount E₁ of the analyte metalspecies may, for example, be defined as in the following equation:E ₁=(P ₁ −B ₁)/B ₁ =P ₁ /B ₁−1

Moreover, a control emission amount E₂ of the control metal species maybe similarly defined as in the following equation:E ₂=(P ₂ −B ₂)/B ₂ =P ₂ /B ₂−1

Then, a corrected value C may be defined as in the following equation:C=E ₁ /E ₂

As above, the analysis emission amount E₁ as the net emission amount isdefined by how many times greater the value obtained by subtracting thebase emission amount B₁ from the peak emission amount P₁ (P₁−B₁) is thanthe base emission amount B₁. However, there is no limitation to such adefinition. For example, the analysis emission amount E₁ may be definedas a value obtained by subtracting the base emission amount B₁ from thepeak emission amount P₁ (P₁−B₁), or may be defined by how many timesgreater the peak emission amount P₁ is than the base emission amount B₁(namely, P₁/B₁). Similar applies in the case of the control emissionamount E₂ described above. For example, out of the above definitions,the definition that obtains the calibration curve with the highestregression coefficient may be adopted.

EXAMPLES

(1) Plasma Spectroscopy Analysis

The emission amount of mercury or lead was measured using plasmaspectroscopy analysis in the following manner using the measurementcontainer.

Urine samples for measurement (samples #1 to #9), a sample twice asdiluted as sample #8 (sample #8-2) and a sample four times as diluted assample #8 (sample #8-4) were measured for Creatinine (Cre)concentration. The creatinine (Cre) concentration is measured using anautomatic analyzer (JCA-BM6010, manufactured by JEOL Ltd.), employing anenzymatic method using a liquid creatinine measurement reagent (DiacolorCRE-V, (trade name) manufactured by Toyobo). Measurement results aregiven in Table 1 below.

TABLE 1 Cre concentration Sample # (mg/dL) 1 156.67 2 60.19 3 29.44 458.55 5 102.90 6 33.57 7 29.72 8 275.95 9 33.84 8-2 147.81 8-4 75.81

In the preparatory process, 8 μL of a 10 ppm aqueous solution ofthallous acetate was dissolved in 776 μL of each of the samples #1 to#9, sample #8-2, and sample #8-4. The concentration of thallous acetatein the urine samples thus became approximately 100 ppb. In this state,500 μL of the urine sample was taken up into a 1.5 mL Eppendorf tube,and 41.9 mg of lithium hydroxide was then added, followed by agitationfor five minutes using a vortex mixer. Then, 25 μL of ethanol was addedand mixed, and 420 μL of the resulting mixture was introduced into themeasurement container 10.

Then, in the concentration process, an electric current was appliedunder the following concentration conditions, with the plasma generatingelectrode 20 serving as the cathode and the non-plasma generatingelectrode 30 serving as the anode, thereby concentrating positive metalions in the vicinity of the plasma generating electrode 20. Note thatthe applied electric current was a constant current and the appliedvoltage fluctuated in response to the resistance of the urine sample.

Concentration Conditions

Applied electric current: 20 mA

Pulse period: 4 seconds

Duty (pulse ratio): 50%

Application duration: 600 seconds

Immediately after the concentration process, in the detection process, avoltage was applied under the following detection conditions but withthe plasma generating electrode 20 serving as the anode and thenon-plasma generating electrode 30 serving as the cathode. The emissionintensity (count value) at each wavelength of the generated plasmaemission was measured. Note that the applied voltage was a constantvoltage, and the applied electric current fluctuated in response to theresistance of the urine sample. The applied electric current was of agreater value than the electric current applied under the concentrationconditions.

Detection Conditions

Applied voltage: 500 V

Pulse period: 50 μs

Duty: 50%

Application duration: 2.5 ms

Note that values obtained by dividing the count values of thecharacteristic peak for mercury at the 254 nm wavelength (see FIG. 4A)and the characteristic peak for lead at the 368 nm wavelength (see FIG.4B) by the background count value were respectively taken as the Hganalysis emission amount (h₀) and the Pb analysis emission amount (p₀).Values obtained by dividing the count values of the characteristic peaksfor thallium at the 276 nm wavelength and the 351 nm wavelength by thebackground count value were respectively taken as a control emissionamount (276) (t₁) and a control emission amount (351) (t₂).

In the correction process, a value obtained by dividing the Hg analysisemission amount (h₀) by the control emission amount (276) was calculatedas an Hg corrected value (h). Similarly, a value obtained by dividingthe Pb analysis emission amount (p₀) by the control emission amount(351) was calculated as a Pb corrected value (p).

(2) Reference Measurement

Mercury reference measurements were taken using a direct thermaldecomposition mercury analyzer (MA-3000, manufactured by NipponInstruments). Namely, 150 μL of distilled water was added to the same 50μL urine samples as employed in the plasma spectroscopy analysis, and 40μL of a 1% L-cysteine solution was also added thereto. The resultingmixtures were then respectively introduced to the measurement boat ofthe above analyzer together with one grain of granular activated carbon,and measurements were taken using the above analyzer to obtain Hgreference measurement values (x_(H)).

Lead reference measurements were outsourced to an external organization,in which Pb reference measurement values (x_(P)) were obtained bypre-processing each urine sample by thermal acid decomposition usingnitric acid and hydrogen peroxide, and then measured using aninductively coupled plasma analyzer (7700x, manufactured by AgilentTechnologies, Inc.).

(3) Measurement Results

The respective values described above are given in Table 2 for mercuryand in Table 3 for lead.

TABLE 2 Reference Analysis Control measurement emission emission Hgcorrected Sample value amount amount value × 100 # (ppb) (x_(H)) (h₀)(276) (t₁) (h = 100 * h₀/t₁) 1 8.14 0.48 6.47 7.36 2 13.65 0.87 4.1521.06 3 5.66 0.46 5.97 7.66 4 4.78 0.27 4.60 5.84 5 13.05 0.74 5.0914.47 6 3.16 0.21 5.16 4.04 7 5.56 0.37 5.40 6.88 8 47.22 2.90 3.9573.47 9 5.11 0.40 5.75 6.89 8-2 23.95 1.39 5.98 23.26 8-4 11.84 0.866.06 14.15

TABLE 3 Reference Analysis Control measurement emission emission Hgcorrected Sample value amount amount value × 100 # (ppb) (x_(p)) (p₀)(351) (t₂) (p = 100 * p₀/t₂) 1 8.50 2.35 17.45 13.458 2 3.40 0.86 13.376.408 3 5.80 1.48 15.71 9.405 4 2.90 0.83 14.80 5.606 5 10.00 1.99 14.4613.760 6 3.00 0.77 13.70 5.604 7 1.40 0.82 15.36 5.359 8 18.00 3.37 9.0737.112 9 1.80 0.73 16.70 4.361 8-2 9.90 2.37 15.15 15.632 8-4 4.55 1.3815.91 8.686

Note that the Hg corrected values (h) in Table 2 are given as 100 timesthe value obtained by dividing the analysis emission amount (h₀) by thecontrol emission amount (276) (t₁) so as to align their decimalpositions with those of the reference measurement values (x_(H)), thesebeing values closer to the true Hg concentration, in order to facilitatecomparison therebetween. Moreover, the Pb corrected values (p) in Table3 are given as 100 times the value obtained by dividing the analysisemission amount (p₀) by the control emission amount (351) (t₂) so as toalign their decimal positions with those of the reference measurementvalues (x_(P)), these being values closer to the true Pb concentration,in order to facilitate comparison therebetween.

Note that out of the above samples, with the exception of sample #8-4,the values given are average values taken over two or three measurementsof the same sample. The value for sample #8-4 was only measured once.

(4) Mercury Measurements

As illustrated in Table 1, out of the samples #1 to #9, sample #8exhibited a much higher creatinine concentration than the others (275.95mg/dL). Moreover, as illustrated in Table 2, the control emission amount(276) (t₁) of sample #8 was 3.95, which was much lower than the averagevalue of 5.32 across the other samples #1 to #7 and sample #9.

Namely, it is conjectured that the control emission amount (276) (t₁) ofsample #8 was suppressed by the high creatinine concentration.Accordingly, it is conjectured that the Hg corrected value (h) that is avalue obtained by dividing the analysis emission amount (h₀) by thecontrol emission amount (276) (t₁) was higher than it was.

FIG. 5A to FIG. 5D depict scatter diagrams using the data given in Table2, and illustrate correspondence relationships between the referencemeasurement values (x_(H)) and the Hg corrected values (h), includingregression lines. FIG. 5A illustrates a correspondence relationshipbetween the reference measurement values (x_(H)) and the Hg correctedvalues (h) for the data in samples #1 to #9. FIG. 5B illustrates similardata to FIG. 5A, but with the data for sample #8 omitted. FIG. 5Cillustrates similar data to FIG. 5A, but with the data for sample #8replaced with the data for sample #8-2. FIG. 5D illustrates similar datato FIG. 5A, but with the data for sample #8 replaced with the data forsample #8-4. Respective correlation coefficients for the regressionlines illustrated in FIG. 5A to FIG. 5D are given in Table 4 below.

TABLE 4 Regression Line (y = ax + b) Deter- Corre- mination lation Stateof coefficient coefficient sample #8 a b (R²) (R) FIG. 5A Undiluted1.5927793 −2.4096596 0.9912733 0.9956271 (#8) FIG. 5B Omitted 1.3471271−0.6778797 0.8793809 0.9377531 FIG. 5C Diluted to 0.9986452 1.61281800.8844891 0.9404728 half strength (#8-2) FIG. 5D Diluted to 1.3119135−0.5245235 0.8859185 0.9412324 one-quarter strength (#8-4)

The determination coefficient (R²) and the correlation coefficient (R)of the regression line illustrated in FIG. 5A for the data employing theundiluted sample #8 are 0.9912733 and 0.9956271, respectively, whichappears to indicate a strong correlation. However, this correlation isthought to be exaggerated due to the data for sample #8, which isillustrated by an arrow in FIG. 5A.

Note that the determination coefficient (R²) of the regression lineillustrated in FIG. 5B in which sample #8 is omitted is reduced to0.8793809 (and the correlation coefficient (R) is reduced to 0.9377531).However, the slope value (a) is changed from 1.5927793 in FIG. 5A to1.3471271 in FIG. 5B, which is closer to 1.

Regarding the regression line illustrated in FIG. 5C in which sample #8is replaced by sample #8-2, which is diluted to half strength (indicatedby an arrow), the determination coefficient (R²) is 0.8844891 (and thecorrelation coefficient (R) is 0.9404728). The correlation is thusstronger than that of the regression line illustrated in FIG. 5B. Theslope value (a) is 0.9986452 that is also closer to 1. Since thecreatinine concentration after dilution is 147.81 mg/dL as given inTable 1, which does not particularly stand out in comparison to thecreatinine concentrations of the other samples, it is thought that theeffect of the creatinine on the plasma emission of the thallium wasaccordingly reduced, resulting in stronger correlation than thatexhibited prior to dilution. This conclusion is also suggested by thevalue 5.98 that is the control emission amount (276) (t₁) for sample#8-2 given in Table 2, which is almost the same level as the averagevalue of 5.32 mentioned earlier.

Regarding the regression line illustrated in FIG. 5D in which sample #8is replaced by sample #8-4, which is diluted to one-quarter strength(indicated by an arrow), the determination coefficient (R²) is 0.8859185(and the correlation coefficient (R) is 0.9412324) that is somewhatlower than that seen in FIG. 5C, and the slope value (a) is 1.3119135that is somewhat steeper than that of FIG. 5C. Note that the creatinineconcentration after dilution is 75.81 mg/dL as given in Table 1, whichis similar to those of the other samples. However, although someimprovement is observed in comparison to FIG. 5A, as given in Table 2,the value of the control emission amount (276) (t₁) for sample #8-4 is6.06, from which, conversely, an increasing trend can be discerned. Itis therefore conjectured that the correlation is somewhat poorer thanthat of the regression line illustrated in FIG. 5C.

(5) Lead Measurements

As illustrated in Table 1, out of the samples #1 to #9, sample #8exhibited a much higher creatinine concentration than the others (275.95mg/dL). Moreover, as illustrated in Table 3, the control emission amount(351) (t₂) of sample #8 was 9.07, which was much lower than the averagevalue of 15.19 across the other samples #1 to #7 and sample #9.

Namely, it is conjectured that the control emission amount (351) (t₂) ofsample #8 was suppressed by the high creatinine concentration.Accordingly, it is conjectured that the Pb corrected value (p) that is avalue obtained by dividing the analysis emission amount (p₀) by thecontrol emission amount (351) (t₂) was higher than it was.

FIG. 6A to FIG. 6D depict scatter diagrams using the data given in Table3, and illustrate correspondence relationships between the referencemeasurement values (x_(P)) and the Pb corrected values (p), includingregression lines. FIG. 6A illustrates a correspondence relationshipbetween the reference measurement values (x_(P)) and the Pb correctedvalues (p) for the data in samples #1 to #9. FIG. 6B illustrates similardata to FIG. 6A, but with the data for sample #8 omitted. FIG. 6Cillustrates similar data to FIG. 6A, but with the data for sample #8replaced with the data for sample #8-2. FIG. 6D illustrates similar datato FIG. 6A, but with the data for sample #8 replaced with the data forsample #8-4. Respective correlation coefficients for the regressionlines illustrated in each of FIG. 6A to FIG. 6D are given in Table 5below.

TABLE 5 Regression Line (y = ax + b) Deter- Corre- mination lation Stateof coefficient coefficient sample #8 a b (R²) (R) FIG. 6A Undiluted1.8635708 −0.1166839 0.9382689 0.9686428 (#8) FIG. 6B Omitted 1.16605112.6313618 0.9704195 0.9850987 FIG. 6C Diluted to 1.2379537 2.42074020.9712705 0.9855306 half strength (#8-2) FIG. 6D Diluted to 1.16555182.7172208 0.9654972 0.9825972 one-quarter strength (#8-4)

The determination coefficient (R²) and the correlation coefficient (R)of the regression line illustrated in FIG. 6A for the data employing theundiluted sample #8 are 0.9382689 and 0.9686428, respectively, whichappears to indicate a strong correlation. However, this correlation isexaggerated due to the data for sample #8, which is illustrated by anarrow in FIG. 6A.

Note that the determination coefficient (R²) of the regression lineillustrated in FIG. 6B in which sample #8 is omitted is increased to0.9704195 (and the correlation coefficient (R) is increased to0.9850987). However, the slope value (a) is changed from 1.8635708 inFIG. 6A to 1.1660511 in FIG. 6B, which is closer to 1.

Regarding the regression line illustrated in FIG. 6C in which sample #8is replaced by sample #8-2 that is diluted to half strength (indicatedby an arrow), the determination coefficient (R²) is 0.9712705 (and thecorrelation coefficient (R) is 0.9855306) and the slope value (a) is1.2379537, which indicate correlation substantially the same as theregression line illustrated in FIG. 6B. Similarly to the case of themercury measurements discussed above, since the creatinine concentrationafter dilution is 147.81 mg/dL as given in Table 1, which does notparticularly stand out in comparison to the creatinine concentrations ofthe other samples, it is thought that the effect of the creatinine onthe plasma emission of the thallium was accordingly reduced, resultingin stronger correlation than that exhibited prior to dilution. Thisconclusion is also suggested by the value 15.15 that is the controlemission amount (351) (t₂) for sample #8-2 given in Table 3, which isalmost the same level as the average value of 15.19 mentioned earlier.

Regarding the regression line illustrated in FIG. 6D in which sample #8is replaced by sample #8-4 that is diluted to one-quarter strength(indicated by an arrow), the determination coefficient (R²) is 0.9654972(and the correlation coefficient (R) is 0.9825972) that is marginallylower than that seen in FIG. 6C, although the slope value (a) is1.1655518 that does not differ greatly to that seen in FIG. 6C. Notethat the creatinine concentration after dilution is 75.81 mg/dL as givenin Table 1, which is similar to those of the other samples. However,although some improvement is observed in comparison to FIG. 6A, as givenin Table 3, the value of the control emission amount (351) (t₂) forsample #8-4 is 15.91, from which, conversely, an increasing trend can bediscerned. It is therefore conjectured that the correlation ismarginally poorer than that of the regression line illustrated in FIG.6C.

(6) Summary as to Dilution of Urine Sample

As described above, it can be seen that the high endogenous creatinineconcentration in urine samples brings down the control emission amountfrom the thallium, thereby increasing the corrected values that directlyaffect the calculation of the mercury or lead concentrations, thushindering accurate measurement. It can thus be seen that diluting theurine sample in order to bring down the endogenous creatinineconcentration reduces the effect on the control emission amount from thethallium.

However, there is a possibility that excessive dilution of the urinesample may be detrimental to the correlation. This is thought to be anissue of balance, since the concentration of the mercury or lead analytealso decreases as a result of dilution. Reducing the concentration ofthe urine sample itself conversely reduces the main factor impedingplasma emission from the thallium, such that it is impossible to ruleout the possibility of increasing the control emission amount from thethallium. Accordingly, in urine samples in which the endogenouscreatinine concentration exceeds approximately 180 mg/dL, it isconsidered preferable that the dilution rate be at least around 1.5times, and not be higher than around 3.5 times at most, thus keeping thedilution rate below 4 times. Alternatively, it is considered preferableto regulate the creatinine concentration after dilution so as to be from75 mg/dL to 180 mg/dL.

In this manner, mercury concentration or lead concentration havingstrong correlation with reference measurement values can be quantifiedby diluting a urine sample in which the endogenous creatinineconcentration exceeds approximately 180 mg/dL by about 3.5 times, or bydiluting the urine samples to no less than 75 mg/dL, while not dilutinga urine sample in which the endogenous creatinine concentration does notexceed 180 mg/dL, and then subjecting the urine sample to plasmaspectroscopy analysis as described above and comparing the obtained Hgcorrected value (h) or Pb corrected value (p) to a calibration curveobtained by advance measurements of known concentrations of mercury orlead.

(7) Emission Spectrum of the Control Metal Species

Note that the actual emission spectrum of thallium as the control metalspecies is illustrated in FIG. 7A. The characteristic peaks of thecontrol wavelengths at three locations, indicated by arrows in FIG. 7A,can be used as control emission amounts. These are enlarged in FIG. 7Bto FIG. 7D, respectively. Namely, the control wavelength of thecharacteristic peak illustrated in FIG. 7B is in the vicinity of 276 nm,and the characteristic peak at this control wavelength forms the basisfor calculating the control emission amount (276) (t₁) suitable formeasuring mercury, as described above. Moreover, the control wavelengthcharacteristic peak illustrated in FIG. 7C is in the vicinity of 351 nm,and the characteristic peak at this control wavelength forms the basisfor calculating the control emission amount (351) (t₂) suitable formeasuring lead, as described above. Note that the control wavelength ofthe characteristic peak illustrated in FIG. 7D is in the vicinity of 378nm. This could conceivably be used as the basis for calculating acontrol emission amount for another analyte metal species.

INDUSTRIAL APPLICABILITY

The present invention may be utilized in a method in which mercury orlead in a urine sample is concentrated on an electrode by stripping, andplasma emission is used to quantify the mercury or lead.

What is claimed is:
 1. A plasma spectroscopy analysis method comprising:a preparatory process of diluting a urine sample assumed to containmercury or lead as an analyte metal species, wherein, in a case in whichan endogenous creatinine concentration in the urine sample exceeds 180mg/dL, the urine sample is diluted such that the creatinineconcentration is from 75 mg/dL to 180 mg/dL, and then adding a knownconcentration of thallium as a control metal species to the dilutedurine sample; a concentration process of introducing the urine samplecontaining the control metal species to a measurement container, andapplying an electric current across a pair of electrodes disposed in themeasurement container to concentrate the analyte metal species and thecontrol metal species present in the urine sample in a vicinity of atleast one of the electrodes; a detection process of applying an electriccurrent across the pair of electrodes after the concentration process soas to generate plasma, and detecting emitted light from the analytemetal species and the control metal species arising due to the plasma; acorrection process of calculating a corrected value by correcting ananalysis emission amount that is a net emission amount at an analysiswavelength corresponding to the analyte metal species detected in thedetection process, using a control emission amount that is a netemission amount at a control wavelength corresponding to the controlmetal species detected in the detection process; and a quantificationprocess of quantifying the analyte metal species in the urine sample bycomparing the corrected value to a calibration curve obtained by advancemeasurements of known concentrations of the analyte metal species. 2.The plasma spectroscopy analysis method of claim 1, wherein, in thecorrection of the correction process, a value obtained by dividing theanalysis emission amount by the control emission amount is taken as thecorrected value.
 3. The plasma spectroscopy analysis method of claim 1,wherein in the detection process, the direction in which the electriccurrent flows be opposite to that in the concentration process.
 4. Theplasma spectroscopy analysis method of claim 3, wherein the electriccurrent may, for example, be set from 0.01 mA to 100,000 mA.
 5. Theplasma spectroscopy analysis method of claim 1, wherein the urine samplecomprises only one of mercury and lead.
 6. The plasma spectroscopyanalysis method of claim 1, wherein in the concentration process, theelectric current applied across the pair of electrodes is from 0.01 mAto 200 mA.
 7. The plasma spectroscopy analysis method of claim 1,wherein the detection process is performed at the same time as theconcentration process ends.
 8. The plasma spectroscopy analysis methodof claim 1, wherein the creatinine concentration is diluted from 1.5times to 3.5 times.
 9. The plasma spectroscopy analysis method of claim1, wherein the control metal species is added such that its finalconcentration in the urine sample is 100 ppb.